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Jeff,


In addition to what has been already suggested I would: 1) Not put any quartz wool on top of the Cr oxide in the combustion/oxidation column; just add 1 more cm of Cr oxide so the quartz insert sits on it, 2) Put less quartz wool (~0.5 cm) but more Cr oxide (0.5 cm) on top at the bottom of the quartz insert, 3) Open/unscrew the purge valve on the autosampler lid very gently, and 4) Use the smallest amounts of sample as possible. We had similar issues 5 years ago and removing the top quartz wool plug from the combustion column made a big difference. Cheers. Mihai


Dr. Mihai Lefticariu

IRMS Scientist

Mass Spectrometry Facility

Neckers 103

Southern Illinois University Carbondale

Carbondale IL 62901

________________________________
From: Stable Isotope Geochemistry <[log in to unmask]> on behalf of Lora Wingate <[log in to unmask]>
Sent: Monday, February 20, 2017 9:00:06 AM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] EA insert fusing to oxidation column

Hi Jeff,
I don't know if this will be helpful or not, but I use a chromium "buffer" (~1/2 cm) below the insert in the oxidation column. And I change the insert every run.
Sorry if this is redundant, I didn't check the entire thread.
Lora


On Sun, Feb 19, 2017 at 2:06 PM, Jeff Havig <[log in to unmask]<mailto:[log in to unmask]>> wrote:
Hello Analytical Experts-

I am running a Costech Elemental Analyzer attached to a Delta V Advantage IR-MS, and have been having issues with the combustion chamber quartz insert fusing to the oxidation column (we have had to the replace the oxidation column three times now because of this, and this is less than ideal).

Our setup:
The insert has ~ 1 cm of quartz wool at the bottom with ~2-3 mm of Chromium(III) oxide on top of that. I have been using the medium (5x9 mm) tin capsules for loading samples (49 per run, 2 to 3 runs per insert). The samples I have been running include volcanically-derived glacial sediments, snow algae, and hot spring biofilms (mostly composed of amorphous silica). Some of the samples have been acidified with HCl to remove DIC and carbonates, but have all been rinsed with 18.2 MOhm/cm water to remove all Cl- before drying and grinding.

It seems as though the insert quartz is fluxing and being stripped away, enlarging the slit openings and weakening the insert, allowing the tin to leave the side slits and fuse the insert to the inside wall of the oxidation column. Also, there seems to be a tendency for yellow-ish melt/precipitate to form at the bottom of the insert, fusing it to the oxidation column there as well. I have attached an image (pdf) of the last failure with examples of what I am trying to describe.

The temperature of the combustion chamber/oxidation chamber is at 1000 C (checked with thermocouple). This has happened a few times in the past, but never consistently like this.

If any of you happen to have had this problem and might know 1) what is going on, and 2) the best way to fix the problem, I would be eternally grateful for your time and help.

-Jeff

--
Jeff Havig, Ph.D.
Adjunct Faculty
Room 517
Geology-Physics Building
Department of Geology
McMicken College of Arts and Sciences
University of Cincinnati
Cincinnati, OH 45221-0013


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--
Lora L. Wingate
University of Michigan
Department of Earth and Environmental Sciences
Stable Isotope Laboratory
1013 C.C. Little Building
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Ann Arbor, MI 48109-1005

phone:  734-763-0561